Coloring of anodized aluminum



United States Patent 3,264,142 LORNG 0F ANQDIZED ALUMINUM Eugene Wainer, Shaker Heights, (lhio, assignor to Horizous incorporated, Cleveland, Ohio, a corporation of New Jersey No Drawing. Filed Feb. 19, 1963, Ser. No. 25%,72? 1 Claim. ((Cl. 148--6.ll)

This invention relates to an improvement of the invention described in my copending application Serial No. 37,042, filed June 20, 1960, and issued as United States Patent 3,079,309 on Feb. 26, 1963, of which the present application is a continuation-in-part. The invention relates to the coloring or decoration of anodized aluminum.

The present invention is directed to an improvement in which the novel technique and compositions described in the aforesaid patent are utilized in cooperation with a specific type of resist to obtain the desired result in a simple and direct manner which improves the practical application of the process.

Briefly in the procedure constituting the present invention a clean aluminum surface which has been anodized in a known manner which yields a porous oxide surface layer, is then printed on using standard office offset equipment with ordinary lithographic inks such as those based on boiled linseed oil and various resins, modified in a manner disclosed below. Thereafter, the printed object is coated with a uniformly applied coating of the compositions described and claimed in the aforementioned patent. After this, the resulting article is baked to desorb the coloring matter from said coating composition into the pores of the anodized article, except in the areas where the lithographic ink resist is present. After removing the powdery residue of the composition which remains after the baking step, the lithographic ink resist is removed by sponging the plate with benzene or other similar hydrocarbon solvent. As a result of this procedure the coloring matter or dye penetrates into the porous anodized surface except in the areas masked by the lithographic ink vehicle which acts as a resist.

Unfortunately when using conventional lithographic inks as the resist, a tendency for bleeding to occur around the edges has been experienced, perhaps because of a tendency for the lithographic inks of the type indicated, to emulsify with the ethylene glycol or other high boiling polyol in the marking compositions.

This bleeding or feathering tendency takes many forms and the adverse results become more sharply defined the thicker and more porous the anodized layer on the aluminum. In considering very thin aluminum foils, it is the usual practice to produce an anodized layer on such foils when considered for decorative purposes only to a thickness of 0.05 to 0.1 mil. When, in addition to the decorative requirement, a more than normal resistance to corrosion is also desired the anodized layer will be produced in a thickness varying in the range between 0.2 and 0.5 mil. When using a normal lithographic ink for the lower thickness the feathering and bleeding noted above takes place to a slight but quite noticeable extent so that the overall effect is a very poor edge to the printed character. When printing with a lithographic ink on the thicker layers followed by dyeing with the glycol type inks the defect is markedly increased in view of the high absorption characteristics of such thicker layers in that not only is the bleeding and feathering of the edge of the character noticeable but undesired low level dyeing takes place right through the resist to an extent where the product is considered completely unacceptable. As indicated previously, it is believed that those adverse effects are due to an increased tendency for the ethyleneglycol ice or other high boiling point polyol in the marking compositions to emulsify with the linseed oil base.

it has now been found that this undesirable manifestation may be completely eliminated by the addition of up to 10% by weight and preferably between 3% and 7% by weight of motor oil or other similar heavy hydrocarbon to the lithographic ink.

The motor oil found most useful for the purposes of the invention is designated in the trade with the viscosity SAE No. 30, this being the medium viscosity grade. When added to the lithographic ink in the preferred ranges indicated above and applied to the thin somewhat less porous layers normally utilized on foil the bleeding, feathering and other defects initially encountered using the lithographic ink as the resist in the presence of the polyol type dyeing agents disappear and a completely acceptable commercial rendition is obtained. However, as the thickness of the anodized layer is increased and the porosity also increased the defect of poor edges and feathering starts to appear again but to a very much diminished extent, than hitherto experienced. It has been found that with these very much thicker layers the defect can again be removed entirely by adding along with the motor oil about 1% of an oil soluble met-a1 stearate, such as barium, calcium, zinc or aluminum. The percentages of stearate added relate to the entire bulk of the lithographic ink resist. A preferred range of stearate addition is between 05 and 3%. Amounts of stearates beyond this percentage have a tendency to cause the ink to liver.

In summary, the #30 motor oil alone is adequate for achieving the desired results on anodized layers having a thickness not greater than 0.1 mil, while for thicknesses greater than this, a combination of the #30 motor oil and the oil soluble metal stearate is required.

The compositions described in the above noted patent application comprise combinations of a liquid base and a coloring matter or color progenitor dissolved in this liquid base, a finely divided inert solid porous pigment, with or without the admixture of viscosity control agents. Minor amounts of water are generally added to the base composition and in order to improve solubility characteristics small amounts of alcohols such as methyl alcohol and ethyl alcohol or simple ketones such as acetone may be added in some instances.

As described in the patent, the base liquid utilized in the composition is an organic hydroxy compound exhibiting a boiling point in excess of C. and which is completely soluble in water. Suitable base liquids include glycerol, the glycols, and the glycol ethers and mixtures thereof. Glycols suitable for the purpose of the invention include the simpler glycols such as ethylene glycol, 1,4-butanediol, 2,3-butanediol, the pentanediols, and the like. Water soluble glycol ethers with suitable boiling points include diethylene glycol monobutyl ether, diethylene glycol monoethyl ether, glycol monobutyl ether, glycol monoethyl ether, and the like. The coloring matter or color progenitor dissolved in this base liquid may be either organic dyes or inorganic compounds which produce a color directly on the anodized layer or provide the possibility of obtaining such a color through double decomposition reactions. The organic coloring matters used are the usual type commonly known in the art for the coloring of anodized aluminum. Such coloring matters are chosen so as to exhibit a relatively high degree of solubility in the liquid vehicles described above. The color substances most commonly used for such purposes are acid types and types which readily form metal complexes. Typical examples of acid types are the dyestuffs Orange 11, Direct Sky Blue, and the like. Other dyes in the same category and identified by their color index number are Acid Orange 80, Acid Orange 62, Acid Red 212, Direct Yellow 5, Direct Blue 79, Acid Black 29. Dyes which (form metal complexes or which mordant with the aluminum hydrate surface contain salicyl groups and similar linkages and are defined by names such as Chrome Fast Orange R, Palatine Bordeaux RN, Color Index No. 27 Mordant Orange, Color Index No. 17 Mordant Brown, Color Index No. 8 Mordant Orange and Color Index No. 33 Mordant Green. All of the water soluble or sparingly soluble organic dyes normally used for the dyeing of anodized layers on aluminum and well known to those skilled in the art are suitable in these compositions. Commonly used inorganic coloring matters may be used. For instance, a metallo-organic compound may be utilized in the composition and driven into the pores and then hydrolyzed in the pores, during sealing, to yield the desired color. Organic salts of such metals as iron, cobalt, nickel, manganese, chromium, vanadium, copper, and the like are utilized and the known materials which are suitable for such hydrolytic deposition include acetates, oxalates, acetyl acetonates, and the like. Colors based on metal salts and utilizing double decomposition reactions may also be applied.

As described in the aforesaid patent it is preferred that a water soluble polyethylene glycol with a molecular weight of from 4000 to 6000 is added to the mixture of base liquid and dye, preferably as a 25% water solution.

The final constituent of the compositions described in said patent is a finely divided inert porous solid pigment, the presence of which provides proper printing, fulling, and body characteristics to the water-compatible base inks. Preferably the pigments chosen are White in color. Colored pigments may be used if desired. The pigments indicated to be most useful in said patent include titanium dioxide, precipitated barium sulfate, a coprecipitate of barium sulfate and titanium dioxide, and to a lesser extent finely ground siliceous minerals such as quartz, nepheline syenite and feldspar. The pigment is chosen so that no chemical reaction takes place at elevated temperature either with the vehicle of the ink or with the coloring matters involved.

The coloring compositions described above are produced as follows: Dealing with inks based on organic dyestuffs, the dye of the particular desired color is added to the base liquid in concentrations ranging between 0.5 and 10% by weight. The base liquid is heated at temperatures not exceeding 100 until the dye has dissolved or dispersed completely and the liquid is then allowed to cool approximately to room temperature. A water solution of polyethylene glycol having a molecular weight in the range of 4000 to 6000 is then added and stirred in until dispersion and solution is complete. The preferred amount of polyethylene glycol to ten parts of polyethylene glycol per 100 parts of base liquid. The dye solution at this stage will vary from a relatively thin liquid to one which is quite viscous depending on the solubility characteristics of the dyestuif originally added. At this stage, the finely divided inert solid pigment is added with vigorous stirring until a consistency suitable for coating is obtained. This is established by achieving a consistency just short of a thick paste in which state the inks can be ground in a muller, ink mill, or a ball mill but will not flow readily if the container is tilted. When titanium dioxide is used as the inert, solid pigment, the amounts utilized for achieving a proper printing consistency are in the range of 60 parts by weight to 130 parts by weight of titanium dioxide for each 100 volumes of base solution. In the case of precipitated barium sulfate, the range varies between 70 parts by weight of precipitated barium sulfate to 140 parts by weight for each 100 volumes of base color solution. In general, the amount of inert pigment needed for fulling purposes varies as a function of its specific gravity. As a final step, the composition is homogenized by passing the mixture through an ink roller mill, grinding in a ball mill or in a muller or similar attrition device.

To utilize the compositions described in my prior application, for the purpose of coloring an anodized aluminum surface, in accordance with the present invention, a design is first printed on the anodized surface using a conventional lithographic ink to which up to 10% by weight of #30 motor oil has been added, or in the case of very thick anodized layers up to 10% by weight of #30 motor oil plus up to 3% by weight of oil soluble metal stearates, barium, zinc and aluminum stearates being preferred. After permitting oxidative drying to harden the lithographic ink to convert the same to a resist as has been practiced in the past, the paste compositions described in my earlier application are applied to the entire surface, by roller coating, doctor blading, dipping or any other conventional coating procedure. The resulting article is then dried at C. until the surface glass disappears due to the elimination of residual water from the paste. This gene-rally requires between five and ten minutes. The resulting product is then heated at temperatures between 25 and 70 C. below the boiling point of the high boiling liquid constituent in the composition. In the case of glycerol, such a temperature would be of the order of 225 C. to 250 C. In those cases where the tinctorial power of the dye is destroyed by maintaining it at this high temperature for too long a period, a lower boiling point liquid is used instead of glycerol. At the temperatures indicated, the glycerol and glycerol type liquids are evaporated completely from the surface in approximately five to eight minutes. The deeply colored ink is replaced with an almost white deposit of the original pigment. The white deposit is brushed from the surface with a soft cloth and it is found that practically all of the coloring matter originally available in the ink has been driven into the pores of the aluminum underneath except where the substrate has been printed with the lithographic ink resist. The inert pigment residue, while soft, is still strong enough to maintain its position so that the plate may be handled with impunity. After the inorganic pigment residue has been removed by wiping, the resist is removed by sponging with benzene or other hydrocarbon solvent. Then a second resist may be printed on the base and a second paste applied to the entire base and heated as described until the second color is printed on. The process is continued until the entire surface is colored with as many colors as may be desired. Finally, the anodized layer and multicolor pattern it now contains is sealed by standard techniques, usually involving immersion in boiling distilled water containing minor amounts of nickel and cobalt acetate.

In the case of dyeing with inorganic salts where a single inorganic salt is utilized as the color agent and subsequently hydrolyzed in the pores as a result of the sealing practice, the procedure as described above is followed in identical fashion.

In the case of dyeing utilizing doubie decomposition reactions, after masking with the lithographic ink resist, the areas to be colored are impregnated with a. brush or sponge. Usually the agent least susceptible to hydrolysis is applied. This is followed by printing the second agent required for formation of the precipitated color in the pores of the aluminum in which such second agent is made up in the paste form described previously.

Regardless of which of the above is utilized, the chalky, dusty deposit remaining after the heating to desorb the coloring agent into the pores of the anodized surface is removed by lightly brushing the surface and then the lithographic ink is removed by a solvent wash. One or more additional colors may be printed by a repetition of the process. Thereafter the colored surface is sealed in the usual way by immersion in a boiling salt solution of the type commonly used in this art.

The following examples are intended to illustrate a preferred mode of practicing the invention.

Example I A lithographic ink is made up by blending 4.5 pounds of cobalt naphthenate (5% C content) and 35 pounds of carbon black into 60.5 pounds of #3 lithographic varnish and thereafter adding pounds of #30 motor oil to the resulting mixture, e.g. on a roller mill. The carbon black in this composition is added to provide the proper body for the lithographic ink and to make the image readily visible for ease of subsequent working. Using a standard lithographic offset press fitted with an aluminum master plate, aluminum foil having an overall thickness of 0.003 mil and an anodized layer thickness of 0.08 mil is imprinted with the modified lithographic ink prepared as described. The sheet is allowed to stand exposed to the air after imprinting for 3 to 4 hours before applying the next step. This is to permit a sufficient amount of oxidat-ive drying to take place so as to reduce the tendency for the image to smear. This step may be hastened by heating for a few minutes in an oven at a temperature between 80 and 100 C.

A p-olyol ink or dyeing composition is then made up by dissolving 2.5 grams of Sandoz aluminum blue B in 100 ccs. of ethyleneglycol at 80 C. After solution is complete, the solution is allowed to cool to room ternperature, after which 5 grams of polyethyleneglycol of approximate molecular weight 4000 dissolved in 20 cos. of water is added with stirring. Thereafter, 135 grams of titanium oxide pigment is stirred into the solution and the batch is then passed through a roller mill to complete the dispersion and insure the elimination of lumps.

This fully dispersed ink composition is then placed in a reverse roller coating mill and a uniform film of the ink deposited over the surface of the previously printed and dried aluminum plate. The reverse roller coating device and press platens are adjusted so that an ink thickness of approximately 0.5 mil is obtained. Immediately after roller coating, the printed and dyed plate is placed in an oven at approximately 85 C. and held at this temperature for 5 minutes, after which the plate is transferred to a second oven maintained at a temperature approximately 150 C. and held at this temperature for another 5 minutes. After removal from the Oven the specimen is inserted in a tank containing benzene and allowed to remain for about 1 minute, after which the surface is rubbed lightly with a sponge until completely clean. The usual practice with this type of ink in the absence of resist is the removal of the soft crust with a dry cloth but it has been found that both the crust and the resist can be removed simultaneously in the benzene washing operation indicated above. The process may now be repeated for the application of other colors as defined in the foregoing. After the last color has been applied by the technique described the aluminum plate is immersed in a standard sealing solution at the boiling point, and the boiling continued for minutes. The sealing solution consists of nickel acetate, cobalt acetate and boric acid in dissolved water. The concentration of the nickel acetate is approximately 6 grams per liter, the cobalt acetate is approximately 1 gram per liter, and the boric acid approximately 8 grams per liter so as to yield a pH between 5 and 6. The overall procedure as given in the sample is completed with the sealing operation, yielding a multicolor, colorfast product in which the colored and uncolored portions of the anodized layer are coplanar with each other so that no relief at all exists between such colored and uncolored areas thus yielding a surface which is particularly resistant toward picking up oil and casual dirt.

Example [I An aluminum plate having a thickness of 0.008" is provided with an anodized layer exhibiting a thickness of 0.3 mil. This is then imprinted on an offset lithographic press with the lithographic ink used in Example I except that 1 pound of barium stearate was added in addition to the #30 motor oil. Thereafter, the process as described in Example I is followed through again yielding a single color or multicolor rendition on the aluminum plate sealed into the pores in which the color and the clear areas of aluminum are coplanar.

Having now described the invention in accordance with the patent statutes it is not intended that the invention be limited except as required by the appended claim.

I claim:

In a method of coloring anodized aluminum in which a coloring composition consisting essentially of a water soluble organic hydroxy compound having a boiling point greater than C., a coloring material dissolved therein, a polyethylene glycol having a molecular weight between 4000 and 6000 as a viscosity control agent compatible with and chemically inert toward the remaining constituents in the composition, and a finely divided fulling agent consisting of porous solid inorganic pigment chemically inert toward the remaining constituents in the composition, and wherein the relative proportion of fulling agent in the printing composition comprises between 60 and parts by weight of fulling agent per 100 parts by volume of the solution of the coloring material in the water soluble organic hydroxy compound and the concentration of coloring material constitutes between 0.5% and 10% by weight of the water soluble organic hydroxy compound is applied to a porous anodized aluminum surface and thereafter the resulting article is heated to a temperature sufiicient to eliminate all liquid from said composition, but below that at which the tinctorial power of the coloring material is adversely alfected, and the article is maintained at said temperature while the coloring material is desorbed from the inert solid pigment and is adsorbed into the pores of said porous anodized aluminum surface, and the remaining solid is then wiped off leaving an anodized article colored in the areas in which said composition was applied; the improvement which comprises applying a coating of a linseed oil based lithographic ink containing up to 10% by weight of a motor oil and up to 1% by weight of an oil soluble metal stearate, said coating being applied as a resist to said porous anodized surface, removing a portion of said coating thereby exposing some of the original substrate; and thereafter applying coloring material to said partly coated partly exposed article in the manner described.

References Cited by the Examiner UNITED STATES PATENTS 1,511,816 lO/l924 Marston 106-28 X 1,578,582 3/1926 Caughlan 106-49 2,150,409 3/1939 Yasoshima. 2,194,911 3/1940 Porter. 2,839,412 6/1958 Igler lO6--28 X 3,079,309 2/ 19 63 Wainer 204-3 8.1 FOREIGN PATENTS 445,242 4/1936 Great Britain. 483,776 4/ 193 8 Great Britain.

ALFRED L. LEAVITT, Primary Examiner. RALPH S. KENDALL, Examiner. 

